The invention relates to a fixator for vertebrae or bone fragments, comprising a rod on which at least one pedicle screw is to be secured. The U-shaped head of the pedicle screw forms a receiving seat for the rod. The rod is held in the receiving seat by a fixing device which comprises a U-shaped clamping yoke whose legs can be connected with positive fit to the head of the pedicle screw and whose bridge holds a fixing screw. In a known spinal column fixator (DE-C 41 07 480) the fixing screw acts directly on the rod lying in the receiving seat. This has the disadvantage that the alternating forces which occur between rod and pedicle screw also act on the screw and may loosen it. This is particularly the case when the direction of the rod does not run exactly perpendicular to the longitudinal direction of the screw, and, as a result, a state of considerable looseness can arise upon relative movements, even when the screw has not moved.
The invention is therefore based on the object of making available a fixator of the type mentioned at the outset, which affords more secure connection between rod and pedicle screw and better mutual alignment to the perpendicular setting.